Hydrodynamic brake with power limitation



a Un ted States Patent [1113,542,168

[ 72] Inventor Helinut Muller I [50] Field of Search 188/90,

lleldenheim, Germany 90A, 264, 264.2, 264.25 {21] Appl. No. 771,589 221Filed Oct. 29, 1968 [561 References CM [45] Patented Nov. 24, 1970UNITED STATES PATENTS gnee Volth Getriebe KG 1,610,830 12/1926 Walker188/90(A)UX P g|fl09II|l9|I6Il7(BN Germ ny 2,667,238 1/1954 Bennettl88/90(A)UX lnomy zn Primary Examiner-George E. A. Halvosa [31] No.$55,644 Attorney-Walter Becker [-54] WITH POWER ABSTRACT: A combinedtorque limitation and a tempera- 5 claims 2 Dnwln n ture limitation of aworking medium for a hydrodynamic l brake to permit a maximum brakinglimitation. The working [52] US. Cl. 188/278 chamber of the brake isequipped with a spring loaded pres- 1 188/264, 188/296, 188/274 surevalve in which the spring preload is reduced thermostati- [51] Int. Cl.Fl6d 57/02 cally with increasing temperature of the working medium.

Patented Nov. 24, 1910 Fig. I

Fig. 2

temperature pressure measuring value transformer II-[1H L t E pressurerelief valve M instance with a rail, vehicle driven by engine, as a rulethis motor cooling installation is also emble heat capacity,

HYDRODYNAMIC BRAKE WITH POWER-LIMITATION tion within the working fluidinto heat'which hasto be carriedaway, If the unit to be' braked isdriven by a;motor which requires a heat exchanger for carrying its lostenergy away, for an internal combustion ployed for carrying away thebraking heat and is correspondingly designed with greater dimensions. Itis merely necessary by means of a liquid-liquid-heat exchanger to conveythe heat of the workingmedium of the brake to the cooling fluid of themotor. In view of the required temperature of operation of the motorcooling fluid, however, it is required that not any high amount ofenergy be conveyed form'the brake per time unit into the coolinginstallation because otherwise the cooling water may be overheated withinherent damage to the motor. The possibility of suchthermal overload ofthe motor cooling installation will become immediately apparent whenconsidering the fact thatwith motor vehicles, as .a rule, thehydrodynamic brakes must be so designed that they will be able, withoutdifficulties, to convert 1.5 times the amount of the full motor powerinto heat. Consequently, with hydrodynamic brakinginstallations, theheat exchanger of which feeds heat into a foreign cooling installation,it is necessary, in view of the requirements of this foreign coolinginstallation, to limit the power required. However, also withindependent hydrodynamic braking installations equipped with a coolinginstallation of their own, it is-necessary to prevent an overheating ofthe working medium in order not to impair the lubricating ability of thesaid working medium.

Devices for limiting the power required of the brake have heretoforebecome known. According to these known devices for limiting the powerrequired of brakes, the braking power was determined by measuring thespeed of the braking'rotor and by measuring the braking moment, and thiscontrol factor was by means of a governor limited in upper direction,for in stance by reducing the filling in the brakeJ'lhe power limitobtained in this way is adjusted once and then remains at its respectiveadjustment. In view of high summer temperatures, soiling of the heatexchanger, etc., this power limit is selected sufficiently low.

Aside from the expense involved in such control mechanism, a device ofthis type has the drawback that the braking power remains fixed, eventhou'ghover the major portion of the year, it would :be possible,without danger, even over a longer period of operation, for instance,when driving downhill, to brake at .a higher limit. inasmuch as thetotal mass of the parts contactedby the cooling fluid and the workingmedia, and since the mass of the cooling fluid, as well as the mass ofthe working medium itself, together have a considerathese parts areable, without dangerous increase in temperature, to absorb a relativelyshort heat shock as'it isencountered when suddenly braking a vehiclewhile driving over a plain terrain. This means that with a retardingbraking operation, a limitation of the power with regard to a thermalload of the installation is not necessary and merely cuts down thecapacity of the installed brakes.

It is, therefore, the object of the present invention to pro-v vide ahydrodynamic brake with a power limitation which will overcome the abovementioned drawbacks. It is another object of this invention to provide adevice as set forth in the preceding paragraphwhich, in order to makefull use of the installed braking power is provided with variable powerlimitatrons.

These and other objects and advantages of the invention will appear moreclearly from the followingspecification in connectionwith theaccompanying drawing in which:

FIG. 1 diagrammatically illustrates, partially in section, ahydrodynamic brake according to the present invention with a brakingpower limiting valve.

FIG. 2 shows the same brake as that illustrated in FIG. 1, but differsfrom FIG. 1 inasmuch asthe braking power limiting valve is of adifferent design. i

The hydrodynamic brake according to the present invention, in view ofthe strength of the gears between the brake and the axle to be braked,makes use of the braking moment, and in view of the lubricating abilityof the working medium employs the temperature of the latter as a meansfor limiting the required power. The hydrodynamic brake according to thepresent invention is characterized by the combined employment of'alimitation of the braking moment and of a temperature limitation of theworking medium in such a way that the working chamber of the brake isequipped with a spring loaded pressure limitingvalve, the spring ofwhich has its preload reduced thermostatically with increasingtemperature of the working medium. Advantageously, the mechanicalcoupling between the thermostat and the spring is so designed thatreduction in the, spring preload starts only from a certain adjustabletemperature.

The invention is based on the assumption which is generally borne out bythe face, at least approximately in the upper range of operation, thatthe torque of the hydrodynamic brake is with constant fillingproportional to the pressure prevailing at the outer circumference ofthe torus shaped working chamber. This pressure is limited by valves.When'the pressure in the working chamber becomes higher than permittedby the spring preload, in other words if the braking moment becomes toohigh, the working medium will displace the valve piston against thethrust of the spring until a new condition of equilibrium has beenestablished, thereby opening up a cross section through which thefilling of the working chamber of the brake will be reduced. In view ofthis reduction in the filling, the braking moment is reduced even thoughthe filling pressure may stay at the increased value which brought aboutthe. reduction of the filling. In view of these steps, mechanical damageto the power transmitting elements between the braking rotor and theaxle to be braked will be practically made impossible.

Since, when engaging the brake, first always the torque becomeseffective in view of the engaged hydrodynamic brake, and the pressure atthe outer circumference of the working chamber becomes effective, first,as the case may be, a corresponding control operation is initiated atthe pressure limiting valve. Thismeans that at the start of the brakingoperation, automatically the maximum permissible braking moment occurs.Only later a thermal action of the braking operation occurs. Dependingon the duration and intensity of said thermal action, additionally tothe effect of the pressure of the working medium, a temperatureinfluence is conveyed to the valve piston, This influence acts with anincrease in the temperature in opening direction, which means that thedegree of filling of the coupling is reduced further. Due to the factthat the torque is limited in conformity with the heat up of the workingmedium, as a whole a limitation in the power is brought about, i

Since the maximum permissible temperature of the working fluid, due toits simultaneous employment as a lubricant, is

generally lower than the maximum permissible temperature of the coolingwater of a possibly subsequent cooling circuit, the temperature of theworking oil is the one which through the intervention of a thermostatacts upon the limiting valve. The limitation of the power of the brakeby means of the heated up working fluid brings about a movable orvariable power limitation since in'view of the device according to theinvention, more braking heat is carried away in winter than is duringsummer time, without unduly exceeding a permissible temperature. Thetemperature, the proper reason for a power limitation has by the presentinvention obtained its proper importance and has been made use of as acontrolling factor in connection with the power limitation.

For purposes of compensating the deviation of the linear connectionbetween braking moment and pressure at the outer circumference of theworking chamber or for purposes of introducing another interdependence,it is suggested according to a further development of the presentinvention,

that in addition to .the spring preload, a further preloading force actsupon the control piston of the pressure limiting valve, especially apressure force which varies according to a certain law with the speed ofthe braking rotor. Expediently, the spring preload of the pressurelimiting valve is, when'a reduction becomes necessary, in view ofatemperature defect reduced hydrostatically, for instance, through anauxiliary piston, while the pressure for actuating said auxiliary pistonis made available by means of a temperature-pressure measured valuetransformer with hydrostatic supply of auxiliary energy.

Referring now to the drawing, corresponding parts in F105, 1 and 2 areprovided with the same reference numerals whereas similar parts to thoseof FIG. 1 have been additionally provided with a prime.

Specifically referring to the drawing, the hydrodynamic brakeillustrated therein has a rotor 1 and a stator 2, both being equippedwith a blade ring 3 and 4 respectively which together form the torusshaped working chamber 3, 4 of the brake 5. The outer circumference ofthe working chamber of the brake is equipped with a pressure limitingvalve 6 in FIG. 1 and with a power limiting valve 6' in H0. 2.

The limiting valve according to FIG. 1 comprises a controlled piston 8which is under the load ofa preloading spring 7. When the valve is inrest position, the piston 8 closes the overflow conduit 9. When thepressure increases in the working chamber beyond the value determined bythe spring preload, the piston 8 leaves its rest position and regains anew equilibrium in a position somewhat further back. In this way, thepiston 8 frees a certain portion of the cross section of the conduit 9and through this free portion the degree of filling of the brake can bereduced and at a lower value can find its new state of rest or inertia.

The magnitude of the degree of filling of the brake 5 and thus of thebraking moment in conformity with the pressure at the outercircumference of the working chamber 3, 4 is determined by the preloadof the spring 7. This spring rests on a second piston 10 which in itsturn is held in an end position by a spring 11 which is stronger thanthe spring 7. A push rod-14 of a wax thermostat 15 acts upon said piston10 through the intervention of a linkage means 12 and an adjusting screw13. Thermostat 15 is through conduit 16 and 17 brought to thetemperature of the flowing off working fluid. The higher the temperatureof the oil becomes, the farther will the wax push the push rod 14 out ofthe thermostat 15. At a certain temperature, the push rod 14 will engagethe lower end of the adjusting screw 13. As the temperature increasesstill further, the piston 10 will be lifted against the thrust of thespring 11. ln this way the preload of the spring 7 is reduced. Thismeans that at the same pressure in the working chamber, the overflowcross section in conduit 9 will be increased, and the degree of flllingand thereby the braking power will be decreased by the influence of thetemperature.

With the limiting valve 6' according to FIG. 2, the influence of thetemperature has been structurally made use of in a different way. Thelimiting valve 6' likewise comprises a piston 8' which is pressed by theforce ofthe preloaded spring 7' into an end position in which theoverflow conduit 9 is closed. By means of a piston rod 12', the piston14 is connected to the piston 8' lnterposed in the overflow conduit 9 isa thermostat 15' which acts upon a temperature-pressure measuring valuetransformer 20. Said transformer 20 is supplied with pressure by thegear pump 21. In the conduit 22 which leads from the transformer 20 tothe pressure chamber of the piston 14', a fluid pressure prevails alwayswhich is proportional to the oil temperature. This proportionality,however, prevails only above a certain temperature. Below saidtemperature the conduit 22 is without pressure. If the oil reaches atemperature in the said range of proportionality, the piston 14' islifted and opens an overflow cross section in conduit 9 whereby thedegree of filling of the brake is reduced. Consequently, the brakingmoment is reduced. Since at the same speed of the braking rotor thepower transformed by ,the brake decreases, also the temperature of theworking medium drops as long as care has been taken for asufficient-flow of the working medium through the brake. Saidtemperature-pressure measuring value transformers are well known in theart and are disclosed, for instance, in French Pat. No. 1,537,518.

The advantages of the brake according to the present invention are seenin the simplicity ofthe limiting devices and above all in the movabilityor variation of. the power limit. As a result thereof, it is notnecessary to maintain a safety distance from the maximum permissiblepower limit with regard to the temperature of the cooling water and theoil. Instead, the installed power can be taken advantage of to its fullextent. During winter time at high cooling capacity, the admissiblebraking power is higher than in summer time. With a retarded brakingoperation over a short period of time, a considerably higher brakingpower is possible than, for instance, with a downhill drive over alonger period of time.

It is, of course, to be understood that the present invention is, by nomeans, limited to the specific constructions shown in the drawings, butalso comprises modification within the scope of the disclosure.

lclaim:

1. A hydrodynamic brake system operable automatically to limit themaximum permissible braking power absorption by a brake, especially forvehicles, which includes: a fluid flow machine having working fluidreceiving chamber means and forming a hydrodynamic brake, dischargeconduit means adapted to communicate with said chamber means fordischarging fluid therefrom, limiting valve means interposed betweensaid chamber means and said discharge conduit means for controllingfluid communication therebetween, preloaded spring means associated withsaid valve means and continuously urging the same to move in thedirection for interrupting said fluid communication, thermostatic meansoperatively connected to said preloaded spring means and operable tocontrol the latter in conformity with the temperature of the fluidpermitted by said valve means to flow from said chamber means to saidconduit means, said fluid flow machine having astator and a rotortogether forming a working fluid receiving chamber, said valve meanshaving a control piston acted upon by said preloaded spring means andcontrolling the passage of fluid from said chamber means to said conduitmeans, said valve means also having a preloading piston with anauxiliary spring acting upon said preloaded spring means for controllingthe preload thereof in conformity with a pressure force varyingaccording to the speed of said rotor, and an additional hydraulic systemcomprising a pressure fluid source and a pressure-temperature valuetransformer, said additional hydraulic system being operable to act uponsaid auxiliary piston in a direction to move said valve means in thedirection opening said discharge conduit means upon sufficient pressurein said conduit means.

2. Hydrodynamic brake system operable automatically to limit the maximumpermissible braking power absorption by a brake, especially forvehicles, which includes: a fluid flow machine having torus shaped fluidreceiving working chamber means and forming a hydrodynamic brake,discharge conduit means adapted to communicate with said chamber meansfor discharging fluid therefrom, limiting valve means arranged at theouter circumference of said torus shaped working chamber means andinterposed between said working chamber means and said discharge conduitmeans for controlling fluid communication therebetween, said limitingvalve means having a control piston acted upon in opening sense bypressure at the outer circumference of said working chamber means,preloaded spring means associated with said control piston of said valvemeans and continuously urging the said control piston to move in thedirection for interrupting said fluid communication, said preloadedspring means resting on a point which is movable to control continuouslythe preload of said preloaded spring means, and thermostatic meansoperatively connected to said point with respect to said preloadedspring meansandloperable to release saidpreloaded spring means inconformity with increaseof the temperature of-the fluid permitted bysaid valve meansto'flo'w from said chamber means to said conduit means.

- 3. A brake system according to claim 2, in which-said thermostaticmeans is adapted to be adjusted soas only at a selected varialiletemperature of the fluid in said conduit" means to act-upon said-pointwith respect to said preloaded spring means in the direction of reducingthe preload thereof. I 4. A brake system according to claim 2, in whichsaid control piston also has a chamber arranged on the one side thereofupon which the saidpreloaded spring meansare effec tivel y acting,saidchamber being adapted to contain liquid tional-hydraulic systembeing operable to act upon said auxiliary piston in a direction to movesaid movable point in the direction opening said discharge conduit meansupon sufficient pressure'in said conduit means.

' 'isof

